The use of pulsed laser deposited seed layers for the aqueous solution growth of highly oriented ZnO nanowires on sapphire substrates at 95 C: Study of their photocatalytic activity in terms of octadecanoic (stearic) acid degradation

Abstract

The photocatalytic activity of ZnO nanowires grown via an aqueous solution approach at 95 C onto sapphire substrates, which were first pre-coated with ZnO seed layers deposited by pulsed laser deposition at various temperatures (400-700 C), was investigated against the degradation of octadecanoic (stearic) acid under UV-A light illumination. The crystallinity of the ZnO seed layers, as well as their growth orientation along the c-axis, increases with deposition temperature. All chemically grown ZnO samples show narrower (0 0 2) reflections with significantly higher intensity than the seed layers deposited by pulsed laser deposition. The grain size, as well as the seed layer roughness, gradually increases with substrate deposition temperature. The nanowires' diameter also rises with seed layer's deposition temperature, ranging from ∼40 ± 15 nm for 400 C to ∼155 ± 65 nm for 700 C. The chemically grown ZnO nanowires exhibit relatively high transmittance values, especially those grown on sapphire substrates, which were pre-coated with seed layers deposited by pulsed laser deposition at 400 and 500 C. All ZnO samples, including seed layers and nanowires' arrays, show very good photocatalytic activity regarding the degradation of octadecanoic (stearic) acid under UV-A light exposure. In specific, the photocatalytic activity of ZnO nanowires' arrays grown on top of a seed layer deposited by pulsed laser deposition at 600 C is quite remarkable, showing the highest stearic acid disappearance rate, i.e., 4.22 × 10 -8 mol/min (formal quantum efficiency = 4.48 × 10-3) at 30 min of UV-A light illumination. © 2013 Elsevier B.V.